The present invention is concerned with improved instrument lighting systems, and is particularly directed to the provision of simple indicator dial illuminating system for instruments employing light emitting diodes for illumination.
Incandescent lamps are usually employed to illuminate cockpit instrument displays, but these lamps generate a considerable amount of heat. This heat has often contributed to the premature failure of internal electronic components used in standard displays. In addition, incandescent lamps consume a great deal of power and are easily damaged by shock and vibration. Accordingly, a more effective, more reliable means of illumination is needed to solve the above problem, particularly in conjunction with an instrument dial display system which provides a high contrast ratio between the dial indicia and dial face background, and which causes the lighted dial indicia and pointer to exhibit a specified brilliance or lighted color presentation.
U.S. Pat. No. 3,732,560 discloses a rotatable drum indicator which uses light emitting diode back lighting, with the drum being molded from suitable near-transparent or highly translucent plastic material. However, the present dial and light-plate designs do not permit a satisfactory lighted display with light emitting diodes in that the white paint or white colored areas in the presently employed silk screen types of dial designs absorb or attenuate too much light and fail to provide a satisfactory lighting presentation with newly developed light sources, particularly light emitting diodes, and such light sources have a much lower intensity than incandescent lamps.
An improved illuminated dial face presentation system is disclosed in my U.S. Pat. No. 4,044,708, comprising a display of an instrument dial face, a light diffuser element, a high light transmission element mounted on the other side of the diffuser element from the instrument dial face display, light emitting diode means mounted in spaced relation to the light transmission element, and reflector means at the rear of the light transmission element for backlighting the instrument dial face display.
One object of the present invention is the provision of improved instrument dial face lighting systems, particularly for aircraft instruments. A further object is to provide simple lighting systems of the above type, utilizing a minimum number of elements and employing light emitting diodes effectively as a source of light, and which offer the advantages of long life, low power consumption and absence of internal heating. Yet another object is the provision of instrument dial face lighting systems, particularly for aircraft instruments, utilizing light emitting diodes as a light source, which provide illuminated dial face displays which satisfy commercial and military color and/or brightness requirements and which exhibit a uniform color and brightness presentation ranging from maximum illumination to brightness levels nearing extinction.